Halloween is a terrible day to be haunted by ghosts, goblins, and ghouls, but there's nothing in the universe more terrifying than a black hole.
Black holes — regions of space where gravity is so strong that no object can escape — have been a hot topic in the news lately. Roger Penrose won half of the 2020 Nobel Prize in Physics for his mathematical research showing that black holes are an inevitable consequence of Einstein's theory of gravity. Andrea Gates and Reinhard Genzel shared the other half as they showed a giant black hole at the center of our galaxy.
There are three reasons why black holes are terrible: if you fall into a black hole left behind by the death of a star, you will be torn apart; the huge black hole seen at the center of all galaxies has an insatiable appetite; and the black hole is where the laws of physics are erased.
Most of the time black holes are inactive, but when they are active and swallow stars and gas, the regions around the black holes are brighter than the entire galaxy they are in. Galaxies with active black holes are called quasars. Although we have learned about black holes over the past few decades, there are still many mysteries to be solved.
Black holes are expected to form when massive stars die. When a star runs out of nuclear fuel, its core collapses to the densest state of matter imaginable, 100 times denser than an atomic nucleus. The density is so great that protons, neutrons, and electrons are no longer discrete particles. Because black holes are dark, they are discovered when they orbit a normal star. The properties of an ordinary star allow astronomers to infer the properties of its dark companion, a black hole.
The first confirmed black hole was Cygnus X-1, the brightest X-ray source in the constellation Cygnus. Since then, about 50 black holes have been found in systems where normal stars orbit black holes. Of the roughly 10 million galaxies scattered throughout the Milky Way, they are the most recent example.
Black holes are graves of matter; Nothing can escape them, not even light. The fate of those who fall into a black hole will be painful "spaghettiization," a point that Stephen Hawking popularized in his book A Brief History of Time. In spaghetti, the intense gravitational pull of a black hole pulls you apart, separating your bones, muscles, muscles, and even molecules. As the poet Dante described in his poem The Divine Comedy, the words on the gates of hell are: All who enter here, give up hope.
Over the past 30 years, observations from the Hubble Space Telescope have shown that all galaxies have black holes at their centers. Larger galaxies have larger black holes.
Nature knows how to make black holes with staggering mass ranges, from stellar corpses with several times the mass of the sun to monsters with tens of billions of times the mass of the sun. It's like the difference between the Apple and the Great Pyramid of Giza.
Just last year, astronomers published the first picture of a black hole and its event horizon, a 7 billion solar mass behemoth at the center of the M87 elliptical galaxy.
It's more than 1,000 times larger than the black hole in our galaxy, and the discoverer of our galaxy's black hole won this year's Nobel Prize. These black holes are dark most of the time, but when their gravitational pull attracts nearby stars and gas, they erupt with intense activity and release large amounts of radiation. The dangers of massive black holes are twofold. If you get too close, a huge gravity will suck you in. If they are in the active quasar stage, you will be hit by high-energy radiation.
How bright are quasars? Imagine hovering over a big city like Los Angeles at night. About 100 million lights in cars, houses and streets in cities correspond to stars in a galaxy. In this analogy, an active black hole is like a 1-inch-diameter light source in downtown Los Angeles, hundreds or thousands of times brighter than an entire city. Quasars are the brightest objects in the universe.
The largest black hole discovered to date has a mass of 40 billion times that of the Sun, or 20 times that of the Solar System. The exoplanets of our solar system orbit once every 250 years, while this more massive object rotates every three months. Its outer rim moves at half the speed of light. Like all black holes, massive black holes are shielded by the event horizon. At their center is a singularity, a spatial point of infinite density. We can't understand the interior of a black hole because the laws of physics fail. Time freezes at the event horizon, and gravity becomes infinite at the singularity.
The good news about massive black holes is that you can survive falling into them. While their gravitational pull is stronger, the tensile force is weaker than a small black hole, and it won't kill you. The bad news is that the event horizon marks the edge of the abyss. Nothing escapes from within the horizon, so you can't escape or report your experience.
According to Stephen Hawking, black holes are slowly evaporating. In the distant future of the universe, long after all the stars have died and galaxies have been squeezed out of view by the accelerated expansion of the universe, black holes will be the last surviving objects.
The largest black hole would take unimaginable time to evaporate, estimated to be 10 to the 100th power, or 100 zeros after 10. The most terrible thing in the universe is almost eternal.